Energy recovering legged robotic device

ABSTRACT

A legged robotic device is disclosed. The legged robotic device can include a plurality of support members coupled together for relative movement defining a plurality of degrees of freedom, which can correspond to degrees of freedom of a human leg. The legged robotic device can also include actuators to apply forces or torques to the support members in the degrees of freedom. In addition, the legged robotic device can include potential energy storage mechanisms associated with the degrees of freedom operable to store potential energy as a result of relative movement of the support members in the degrees of freedom and to provide at least a portion of the stored potential energy to the support members as compensating forces or torques to assist the actuators. In one aspect, elastic potential energy can be stored. A spring rate and/or a zero position of the potential energy storage mechanisms can be dynamically variable.

RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.14/704,872, filed May 5, 2015, entitled “Energy Recovering LeggedRobotic Device” which claims the benefit of U.S. Provisional ApplicationSer. No. 61/989,427, filed May 6, 2014, and entitled, “Energy EfficientLegged Exoskeleton Having Energy Recovery Elements” each of which isincorporated by reference in its entirety herein.

BACKGROUND

A wide variety of exoskeleton, humanoid, and other legged robot systemshave been disclosed, although not many have actually been constructed.The fundamental technical problem to be solved for such systems, whereenergetic autonomy is concerned, is power. Two options are available:use a high-output power supply that efficiently uses an energy densesource and that can meet the demands of the robotic system, or use lesspower. The first option lacks practicality, inasmuch as portable powerremains a challenge, which leaves the second option. Accordingly, theexoskeletons or ambulatory robots in existence are not capable ofproviding high force and high speed outputs for prolonged periods oftime. In other words, the power issue has been an insurmountableobstacle, with the typical solution being to reduce the power outputcapabilities of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the invention will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate, by way of example,features of the invention; and, wherein:

FIGS. 1A and 1B are illustrations of a legged robotic device inaccordance with an example of the present disclosure,

FIG. 2A is an illustration of an actuator and potential energy storagemechanism configuration in accordance with an example of the presentdisclosure.

FIG. 2B is an illustration of an actuator and potential energy storagemechanism configuration in accordance with another example of thepresent disclosure.

FIG. 2C is an illustration of an actuator and potential energy storagemechanism configuration in accordance with yet another example of thepresent disclosure.

FIG. 3A is an illustration of a valve arrangement that can be used tocontrol hydraulic and/or pneumatic components of a legged robotic devicein accordance with an example of the present disclosure.

FIG. 3B is an illustration of a valve arrangement that can be used tocontrol hydraulic and/or pneumatic components of a legged robotic devicein accordance with another example of the present disclosure,

FIG. 3C is an illustration of a valve arrangement that can be used tocontrol hydraulic and/or pneumatic components of a legged robotic devicein accordance with yet another example of the present disclosure,

FIG. 4 is a graph of a typical human walking gait cycle for the kneejoint showing the relationship between knee torque and knee angle.

FIGS. 5A and 5B are illustrations of a legged robotic device inaccordance with another example of the present disclosure.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION

As used herein, the term “substantially” refers to the complete ornearly complete extent or degree of an action, characteristic, property,state, structure, item, or result. For example, an object that is“substantially” enclosed would mean that the object is either completelyenclosed or nearly completely enclosed. The exact allowable degree ofdeviation from absolute completeness may in some cases depend on thespecific context. However, generally speaking the nearness of completionwill be so as to have the same overall result as if absolute and totalcompletion were obtained. The use of “substantially” is equallyapplicable when used in a negative connotation to refer to the completeor near complete lack of an action, characteristic, property, state,structure, item, or result.

As used herein, “adjacent” refers to the proximity of two structures orelements. Particularly, elements that are identified as being “adjacent”may be either abutting or connected. Such elements may also be near orclose to each other without necessarily contacting each other. The exactdegree of proximity may in some cases depend on the specific context.

An initial overview of technology embodiments is provided below and thenspecific technology embodiments are described in further detail later.This initial summary is intended to aid readers in understanding thetechnology more quickly but is not intended to identify key features oressential features of the technology nor is it intended to limit thescope of the claimed subject matter.

In order to improve an exoskeleton, humanoid, or other legged robotsystem's power output and endurance capabilities with limited poweravailable, the efficiency of such systems must be one of the focuses ofimprovement. Accordingly, a legged robotic device is disclosed thatimproves efficiency over a typical robotic system. In one aspect, apotential energy storage mechanism is included to store energy thatwould otherwise be lost and provide the stored energy for use by thedevice. The legged robotic device can include a plurality of supportmembers coupled together for relative movement defining a plurality ofdegrees of freedom, at least one of the plurality of degrees of freedomcorresponding to at least one degree of freedom of a human leg. Thelegged robotic device can also include an actuator to apply a force or atorque to the support members in the at least one of the plurality ofdegrees of freedom. Additionally, the legged robotic device can includea potential energy storage mechanism associated with the at least one ofthe plurality of degrees of freedom operable to store potential energyas a result of relative movement of the support members in the at leastone of the plurality of degrees of freedom and to provide at least aportion of the stored potential energy to the support members as acompensating force or torque to assist the actuator. A spring rateand/or a zero position of the potential energy storage mechanism can bedynamically variable.

In one aspect, a legged robotic device is disclosed that can include afirst support member coupled to a second support member for relativemovement defining a first degree of freedom corresponding to a degree offreedom of a knee of a human leg. The legged robotic device can alsoinclude a first actuator to apply a force or a torque to the first andsecond support members in the first degree of freedom. In addition, thelegged robotic device can include a first potential energy storagemechanism associated with the first degree of freedom operable to storepotential energy as a result of relative movement of the first andsecond support members in the first degree of freedom and to provide atleast a portion of the stored potential energy to the first and secondsupport members as a compensating force or torque to assist the firstactuator. A spring rate and/or a zero position of the first potentialenergy storage mechanism can be dynamically variable.

In yet another aspect, a legged robotic device is disclosed that caninclude a first support member coupled to a second support member forrelative movement defining a first degree of freedom corresponding to adegree of freedom of a hip of a human leg. The legged robotic device canalso include a first actuator to apply a torque to the first and secondsupport members in the first degree of freedom. Additionally, the leggedrobotic device can include a first potential energy storage mechanismassociated with the first degree of freedom operable to store potentialenergy as a result of relative movement of the first and second supportmembers in the first degree of freedom and to provide at least a portionof the stored potential energy to the first and second support membersas a compensating torque to assist the first actuator. A spring rateand/or a zero position of the first potential energy storage mechanismcan be dynamically variable.

One example of a legged robotic device 100 is illustrated in FIGS. 1Aand 1B. The legged robotic device 100 can be configured as anexoskeleton structure for attachment to a human body, as a humanoidrobot or any other legged robotic device and can be used in applicationsrelevant to the military, first responders, the commercial sector, etc.The legged robotic device 100 can comprise any suitable configuration inaccordance with the concepts discussed herein. In one example, asillustrated in the figures, the legged robotic device 100 can comprise aplurality of support members 110 a-g coupled together for relativemovement defining a plurality of degrees of freedom. For example, thesupport members 110 a-g can be rotatably coupled together definingrotational degrees of freedom about one or more axes 111 a-g, althoughtranslational degrees of freedom are possible. In one aspect, two ormore of the support members 110 a-g can be coupled together at a joint.A joint can accommodate one or more degrees of freedom. For example, thesupport members 110 b, 110 c can be coupled together to form a singledegree of freedom and the support members 110 f, 110 g can be coupledtogether (i.e., by a universal or ball joint) to form degrees of freedomabout axes 111 f, 111 g. Such single or multi-degree of freedom jointscan be provided at any suitable location of the device 100. One or moreof the degrees of freedom, such as the rotational degrees of freedomabout the axes 111 a-g, can correspond to one or more degrees of freedomof a human leg 101, such as hip flexion/extension, hipabduction/adduction, hip medial/lateral rotation, kneeflexion/extension, ankle flexion/extension, ankle inversion/eversion,and ankle medial/lateral rotation.

For example, as illustrated in the figures, the support member 110 e canbe coupled to the support member 110 d for relative movement defining adegree of freedom corresponding to a degree of freedom of a knee (i.e.,knee flexion/extension). The support member 110 c can be coupled to thesupport member 110 d for relative movement defining a degree of freedomcorresponding to a degree of freedom of a hip (i.e., hip medial/lateralrotation). The support member 110 b can be coupled to the support member110 c for relative movement defining a degree of freedom correspondingto another degree of freedom of the hip (i.e., hip flexion/extension).The support member 110 a can be coupled to the support member 110 b forrelative movement defining a degree of freedom corresponding to a yetanother degree of freedom of the hip (i.e., hip abduction/adduction).

A human user or operator may use or interact with the legged roboticdevice 100 by placing his or her feet into a foot portion 107 of thedevice, where the feet of the operator can be in contact with acorresponding force sensor. Portions of the human operator can also bein contact with force sensors disposed on various locations of thelegged robotic device 100. For example, a hip portion 102 of the leggedrobotic device 100 can have a force sensor configured to interact withthe operator's hip. The operator can be coupled to the legged roboticdevice 100 by a waist strap 103 or other appropriate coupling device.The operator can be further coupled to the legged robotic device 100 bya foot strap 104. In one aspect, a force sensor can be located about aknee portion 105 of the legged robotic device 100 near a knee of theoperator. While reference is made to force sensors disposed at specificlocations on or about the legged robotic device 100, it should beunderstood that force sensors can be strategically placed at numerouslocations on or about the legged robotic device 100 in order tofacilitate proper operation of the legged robotic device 100.

The legged robotic device 100 can also comprise one or more actuators112 a-g to apply a force or a torque to the support members 110 a-g inthe degrees of freedom, such as any of the rotational degrees of freedomabout the axes 111 a-g. For example, as illustrated in the figures, theactuator 112 a can apply a force or a torque to the support members 110a, 110 b in the degree of freedom about the axis 111 a. The actuator 112b can apply a force or a torque to the support members 110 b, 110 c inthe degree of freedom about the axis 111 b. The actuator 112 c can applya force or a torque to the support members 110 c, 110 d in the degree offreedom about the axis 111 c. The actuator 112 d can apply a force or atorque to the support members 110 d, 110 e in the degree of freedomabout the axis 111 d. The actuator 112 e can apply a force or a torqueto the support members 110 e, 110 f in the degree of freedom about theaxis 111 e. The actuator 112 f can apply a force or a torque to thesupport members 110 f, 110 g in the degree of freedom about the axis 111f. The actuator 112 g can apply a force or a torque to the supportmembers 110 f, 110 g in the degree of freedom about the axis 111 g.

In addition, a potential energy storage mechanism 113 a-g can beassociated with one or more of the degrees of freedom, such as any ofthe rotational degrees of freedom about the axes 111 a-g. The potentialenergy storage mechanisms 113 a-g can be operable to store potentialenergy as a result of relative movement of the support members 110 a-gin the degrees of freedom and to provide at least a portion of thestored potential energy to the support members 110 a-g as a compensatingforce or torque to assist the actuators 112 a-g. For example, asillustrated in the figures with regard to a degree of freedomcorresponding to knee flexion/extension, the potential energy storagemechanism 113 d associated with the degree of freedom about the axis 111d can be operable to store potential energy as a result of relativemovement of the support members 110 d, 110 e in the degree of freedomand to provide at least a portion of the stored potential energy to thesupport members 110 d, 110 e as a compensating force or torque to assistthe actuator 112 d.

With regard to degrees of freedom corresponding to hip degrees offreedom, the potential energy storage mechanism 113 c associated withthe degree of freedom about the axis 111 c can be operable to storepotential energy as a result of relative movement of the support members110 c, 110 d in the degree of freedom and to provide at least a portionof the stored potential energy to the support members 110 c, 110 d as acompensating force or torque to assist the actuator 112 c. The potentialenergy storage mechanism 113 b associated with the degree of freedomabout the axis 111 b can be operable to store potential energy as aresult of relative movement of the support members 110 b, 110 c in thedegree of freedom and to provide at least a portion of the storedpotential energy to the support members 110 b, 110 c as a compensatingforce or torque to assist the actuator 112 b. The potential energystorage mechanism 113 a associated with the degree of freedom about theaxis 111 a can be operable to store potential energy as a result ofrelative movement of the support members 110 a, 110 b in the degree offreedom and to provide at least a portion of the stored potential energyto the support members 110 a, 110 b as a compensating torque to assistthe actuator 112 a. With regard to degrees of freedom corresponding toankle degrees of freedom, the potential energy storage mechanism 113 eassociated with the degree of freedom about the axis 111 e can beoperable to store potential energy as a result of relative movement ofthe support members 110 e, 110 f in the degree of freedom and to provideat least a portion of the stored potential energy to the support members110 e, 110 f as a compensating force or torque to assist the actuator112 e. The potential energy storage mechanism 113 f, 113 g associatedwith the degrees of freedom about the axes 111 f, 111 g can be operableto store potential energy as a result of relative movement of thesupport members 110 f, 110 g in the degrees of freedom and to provide atleast a portion of the stored potential energy to the support members110 f, 110 g as a compensating force or torque to assist the actuators112 f, 112 g.

Thus, upon putting energy into the potential energy storage mechanisms113 a-g (e.g., such as bending the leg at the knee joint), at least aportion of the energy can be recovered and applied to the load. Forexample, in an upright position or non-energized state, the user orwearer would not feel the load as the load is transferred through thesupport members to the ground. As the potential energy storagemechanisms 113 a-g are energized (e.g., when the wearer bends down),energy is put into the potential energy storage mechanisms 113 a-g. Uponrelease, or upon the user standing upright, the energy is recovered, andput back into the load. This is one example of a situation wherepotential energy storage mechanisms 113 a-g can be used to reduce theamount of work done by the robotic device. In other words, the user isusing his gravity induced weight to put energy into the potential energystorage mechanisms 113 a-g. When it is desired to get the energy back,the user stands or otherwise moves to extract energy from, orde-energize, the potential energy storage mechanisms 113 a-g so now theamount of work the user and the robotic device needs to do is reduced bythe amount of energy put into the potential energy storage mechanisms113 a-g. Stated differently, energy put into the potential energystorage mechanisms 113 a-g can be retrieved or recovered and used toassist the actuators 112 a-g, thereby reducing energy consumption bypreserving energy for use that would otherwise have been wasted.Providing the legged robotic device 100 with potential energy storagemechanisms 113 a-g can therefore increase efficiencies of the device.

The actuators 112 a-g can comprise any suitable actuator, such as ahydraulic actuator, a pneumatic actuator, and/or an electric actuator.In one aspect, an actuator can be remotely located relative to the jointor degree of freedom in which the actuator will provide force or torque.For example, an actuator for an ankle degree of freedom can be locatedon a support member near a pelvis or thigh of the user, and can have apower transfer mechanism, such as a cable routed through a neutral axisof an intermediated degree of freedom (e.g., knee flexion/extension), toremotely actuate the ankle degree of freedom. Such a configuration canlocate the mass of the actuator near a center of rotation (i.e., thehip) to reduce the distal mass and moment of inertia of a legged roboticdevice.

The potential energy storage mechanisms 113 a-g can comprise anysuitable type of potential energy storage mechanism and can be energizedin any suitable manner. In one aspect, the potential energy storagemechanisms 113 a-g can comprise any suitable spring, such as a tensionspring, a compression spring, a torsion spring, a spiral torsion spring,a pneumatic spring (e.g., air or nitrogen cylinder), a cantileverspring, a constant force spring, a negator spring, an elastomericmaterial, a volute spring, a coil spring, a flat spring, a hydraulicaccumulator, a magnetic spring, and/or a bow spring. In another aspect,the potential energy storage mechanisms 113 a-g can comprise anysuitable material or medium to facilitate potential energy storage andrecovery. Thus, a solid elastic member (e.g., made of spring steel orelastomeric material) and/or a pneumatic spring utilizing a gas can beutilized. In other words, any type of spring element can be used thatcan store energy and provide the stored energy to exert a force and/or atorque on support members or assist an actuator. As described furtherbelow, the potential energy storage mechanisms 113 a-g can be configuredto store elastic potential energy and can have elastic behaviorsdynamically modified or tuned to achieve a desired result for a givenapplication or scenario. In addition, energy dissipation characteristicsof the potential energy storage mechanisms 113 a-g can also be varieddynamically.

In one aspect, one or more of the actuators 112 a-g can be undersized(e.g., having less output capabilities than would otherwise be needed)for a maximum load requirement as compared to the size of the actuatorsneeded without the existence of the potential energy storage mechanism.For example, by incorporating and using potential energy storagemechanisms 113 a-g as described herein, an actuator can be sized toprovide approximately half of the maximum force or torque requirementfor a given degree of freedom. This reduction in actuator capability canreduce the size of the actuators as well as the power required tooperate the actuators. It should be recognized, however, that theactuators of any suitable capability can be utilized. A power source 106to power the actuator and/or other components of the legged roboticdevice 100 (i.e., electronics) can be supported about the roboticdevice, such as on an attached framework or in a storage or cargofeature of the legged robotic device 100.

In one aspect, each of the potential energy storage mechanisms 113 a-gcan be combined or associated with an actuator. For example, theactuator 112 b and the potential energy storage mechanism 113 b can belocated at the hip, such as associated with a hip flexion/extensiondegree of freedom of the user's leg. The actuator 112 b can be actuatedto energize the potential energy storage mechanism 113 b, such as whenthe user lifts the leg in hip flexion to ascend a step. In other words,when the actuator 112 b is actuated to lift the leg, energy is put intothe potential energy storage mechanism 113 b, thus energizing thepotential energy storage mechanism 113 b. This energy can be recoveredto assist the actuator 112 b in extending the leg at the hip to raisethe operator and the device 100 onto the step. Thus, energy can be putinto the potential energy storage mechanisms 113 a-g while alsoactuating the leg of the robot and the user's leg. The legged roboticdevice 100 can be configured to provide energy storage/recovery alone orenergy storage/recovery coupled with actuation to make the user moreefficient and stronger. For example, a user can be more efficient atcarrying a load, more efficient at walking, more efficient at climbing,more efficient at running, etc.

In one aspect, an actuator and a potential energy storage mechanism canbe combined into a unit or module that can be disposed or located at adesired joint or coupling of support members of the legged roboticdevice 100. For example, the actuator 112 d and the potential energystorage mechanism 113 d can be combined into a single unit or module andcan have a common housing and standardized interfaces for coupling withsupport members. In one aspect, an actuator and a potential energystorage mechanism can be specifically configured for use with a degreeof freedom corresponding to a particular degree of freedom of the leg,as described in more detail below. For example, the actuator 112 d andthe potential energy storage mechanism 113 d can be configuredspecifically for use with a joint forming a degree of freedomcorresponding to knee flexion/extension. Such modules can also betailored for the hip and ankle degrees of freedom.

In one aspect, the potential energy storage mechanisms 113 a-g can beconfigured to bias the legged robotic device 100 into an upright,standing position, thus making the standing position the defaultposition. This can make the device more convenient to don and doff aswell as increase safety because the device will not collapse with a lossof power. In a particular aspect, the potential energy storagemechanisms 113 a-g can be configured such that the actuators 112 a-gmust be actuated or engaged to accomplish a motion, in addition to forceprovided by the user. For example, the potential energy storagemechanisms 113 a-g can be configured such that the actuators 112 a-g arecaused to be actuated or engaged to accomplish a squat motion, inaddition to the downward force exerted by gravity from the user. Such aconfiguration of the potential energy storage mechanisms 113 a-g canreduce the required output capacity of the actuators 112 a-g to what isrequired to compensate for inertially induced loads or changes inoverall potential energy of the system, rather than to compensate forthe weight of the system itself. This reduced output capacity of theactuators can lead to reduced actuator size and weight as well as theassociated actuator systems (e.g., hydraulic pumps, valves, lines,etc.), which can reduce or minimize the weight of the overall leggedrobotic device 100, thereby reducing power consumption and improvingefficiency.

The use of the potential energy storage mechanisms 113 a-g can have abroad span in terms of increasing a person's capability. The potentialenergy storage mechanisms 113 a-g can be used to increase a user'scapability of carrying loads, to increase the user's endurance with orwithout loads, to facilitate a user being able to run as fast or fasterthan normal, to walk more efficiently, etc. These are all variables andbenefits the potential energy storage mechanisms 113 a-g allows to beintroduced into the robotic device. In addition, using potential energystorage mechanisms 113 a-g the robot can be configured to perform afunction of energy in and energy out at a higher frequency than wouldotherwise be possible. In one aspect, the actuators 112 a-g and/or thepotential energy storage mechanisms 113 a-g can be configured to recoverenergy or facilitate energy extraction, which can be used whendecelerating the support members 110 a-g of the legged robotic device100, particularly when loaded. For example, during normal human walkingthe knee joint follows knee joint torque versus position trajectories(see FIG. 4) where the actuator torque decelerates the joint angularand/or linear velocity. When this happens, energy may be dissipated byan energy dissipation mechanism as described herein, such as a brake(e.g., clutch), a pneumatic mechanism, a hydraulic mechanism, etc.Alternatively, this energy can be stored in the potential energy storagemechanisms 113 a-g as described herein, such as a spring, a pneumaticmechanism, a hydraulic mechanism, etc., and reused later, therebyincreasing the system efficiency.

The potential energy storage mechanisms 113 a-g facilitates a reductionin energy consumption by the robot. Without the potential energy storagemechanisms 113 a-g, all the energy would have been generated anew andmuch wasted. The legged robotic device 100 of the present disclosure issimilar to the human body having tendons and ligaments that function aspotential energy storage/recovery elements. For example, when a personjumps energy is extracted out of the potential energy storage/recoveryelements (tendons, ligaments, and bones). In addition, when a personflexes muscles, energy is being put into the potential energystorage/recovery elements (tendons and ligaments and bones), later to beextracted. In this way, the human body is able to achieve higher rateand higher load performance. One example of this is moving the arm in amanner so as to put elastic potential energy into the tendons,ligaments, and muscles of the shoulder to optimize the throwing of aball at a higher speed. The robot of the present disclosure can beconfigured to function in a similar manner.

In another aspect, the robot can be configured to perform variousregimes and cross regimes. For example, the robot can be configured withpotential energy storage mechanisms 113 a-g that are tailored to aperson's performance in various regimes and cross regimes, such as apotential energy storage mechanism used for walking, but which is alsogood for helping carrying a load. In some cases, potential energystorage mechanisms that facilitate high rate motions may be inconsistentwith potential energy storage mechanisms needed for lower rate motions,so it is contemplated that the robot can comprise a strategic number andtype of potential energy storage mechanisms, and that these can bestrategically implemented and located.

FIGS. 2A-20 illustrate several examples of actuator and potential energystorage mechanisms configurations that can be utilized in the leggedrobotic device 100 of FIGS. 1A and 1B. For example, as shown in FIG. 2A,an actuator 212 and a potential energy storage mechanism 213 can bearranged in parallel. This configuration can be well-suited to provide apreload force or torque to counteract a moment inherent in the leggedrobotic device as a result of the relative positioning of the deviceabout the human user. In one aspect, coupling locations of supportmembers may be laterally offset about the user to form degrees offreedom corresponding to hip abduction/adduction and hip medial/lateralrotation, for example, which may induce moments at the couplinglocations. Utilizing the potential energy storage mechanism 213 toprovide a preload force or torque to support members can thereforefacilitate operating a legged robotic device at lower pressure and/orfacilitate use a smaller, more efficient actuator. Although thisconfiguration can be utilized at any suitable location, thisconfiguration can be particularly beneficial at degrees of freedomcorresponding to hip flexion/extension, hip abduction/adduction, and/orhip medial/lateral rotation. As described in more detail below, suchforce or torque preload bias, as well as the compliance of the potentialenergy storage mechanism 213, can be dynamically tunable to achieve adesired result. FIG. 2A also illustrates an additional or alternativepotential energy storage mechanism 213′, which may be of any suitableconfiguration described herein, arranged in series with the actuator212. Thus, potential energy storage mechanisms can be arranged in seriesand/or in parallel with an actuator at any given joint.

In one aspect, the actuator 212 can be a hydraulic actuator, which canbe configured as a double acting actuator with fluid couplings A, B to achamber 214 on opposite sides of a piston 215. The A and B sides of theactuator 212 can be controlled with one or more valves, examples ofwhich are illustrated in FIGS. 3A-30, to control operation of theactuator 212. In one aspect, the actuator 212 can be selectivelydisengaged or configured for free and unrestrained movement, such as byoperation of a valve. In another aspect, the hydraulic actuator can beconfigured to selectively function as a hydraulic damper. Thus, the samedevice or component can be utilized alternately as an actuator and adamper to control movement of support members in a degree of freedom ofthe legged robotic device.

The potential energy storage mechanism 213 can comprise any suitabletype of spring in any combination. In one aspect, a spring rate of thepotential energy storage mechanism 213 can be dynamically variable. Thespring rate of the potential energy storage mechanism 213 can bedynamically changed in any suitable manner. For example, a constraintlocation on a mechanical spring can vary to effectively change thespring rate. For instance, a spring cantilevered from a support can beconstrained at a variable distance from the support in order to changethe spring rate. A spiral torsion spring can be similarly constrained tochange the spring rate. In a particular example, potential energystorage mechanism 213 can comprise a negator-type spring locatedco-axially with a joint axis. Such a spring has the benefit ofaccommodating adjustable tension to allow the user to tune the springtension to optimize the elastic behavior with a given load.

In one aspect, a zero position of the potential energy storage mechanism213 can be dynamically variable. For example, one or both of anchorlocations 223 a, 223 b can be moved to adjust a zero or neutral positionof the potential energy storage mechanism 213. The position of theanchor locations 223 a, 223 b can be controlled by one or more actuators220 a, 220 b. Dynamically changing the zero position can thereforechange a position at which the potential energy storage mechanism 213will begin to store energy and a position at which the stored energywill be depleted. Thus, dynamically changing the zero position of thepotential energy storage mechanism 213 can influence the relativemovement of support members, which can be manipulated to advantage inimproving performance of the legged robotic device. In one aspect,changing a relative position of the anchor locations 223 a, 223 b canstore or release energy independent of relative movement of the supportmembers. In another aspect, changing a relative position of the anchorlocations 223 a, 223 b can vary a preload in the potential energystorage mechanism 213. Thus, the preload of the potential energy storagemechanism 213 can be dynamically variable.

In one aspect, one or both of the actuators 220 a, 220 b can serve as orrepresent a damper to resist movement of the support members in a degreeof freedom. Any suitable damper can be utilized, such as a hydraulicdamper, a pneumatic damper, a mechanical damper, and/or an electricaldamper (e.g., an electrical generator). In a particular aspect, adamping coefficient of the damper can be dynamically variable, such asby controlling flow through the damper with one or more valves. Theability to dynamically vary the characteristics and functions of theactuator 212 and the potential energy storage mechanism 213 can enabletunable energy storage/recovery and actuation capabilities.

As shown in FIG. 2B, a potential energy storage mechanism 313 can bearranged in series with a clutch 318. The potential energy storagemechanism 313 and the clutch 318 can be arranged in parallel with anactuator 312. This configuration can be used to allow potential energyto be stored and recovered during part of a gait cycle, and permitsupport members to follow a quasi-ballistic (passive dynamics) torqueversus joint angle trajectory (e.g. during leg swing). Thus, althoughthis configuration can be utilized at any suitable location, thisconfiguration can be utilized effectively for degrees of freedomcorresponding to knee flexion/extension and/or hip flexion/extension dueto the ease of dynamically tuning compliance with this configuration.FIG. 2B also illustrates an additional or alternative potential energystorage mechanism 313′, which may be of any suitable configurationdescribed herein, arranged in series with the actuator 312. Thus,potential energy storage mechanisms can be arranged in series and/or inparallel with an actuator at any given joint.

In one aspect, the clutch 318 can be used to selectively engage anddisengage the potential energy storage mechanism 313. The actuator 312can be selectively disengaged or configured for free and unrestrainedmovement. For example, a hydraulic actuator can be configured tofacilitate free movement of a piston 315 within a chamber 314 of thehydraulic actuator 312 to selectively disengage the hydraulic actuator.Thus, selective disengagement of the potential energy storage mechanism313 and the hydraulic actuator can facilitate free relative movement ofthe support members in a degree of freedom.

The clutch can be any suitable type of clutch. Although not explicitlyshown in this figure, the spring rate, zero position, and/or preload ofthe potential energy storage mechanism 313 can be varied, as describedabove with reference to FIG. 2A.

FIG. 2C illustrates an actuator 412 and a potential energy storagemechanism 413 arranged in parallel. As with other examples, the actuator412 can be a hydraulic actuator, which can be selectively disengaged orconfigured for free and unrestrained movement and/or serve as a damper,such as by controlling the movement of a piston 415 within a chamber 414by fluid controlled by one or more valves. The potential energy storagemechanism 413 is shown as a pneumatic spring. The pneumatic spring canbe configured with fluid couplings to a chamber 416 on opposite sides ofa piston 417. Gas can be introduced or evacuated from the chamber 416using one or more valves 424, 425. The valve 424 can be a three-wayvalve connecting the pneumatic spring to a pressure source and a returntank. The valve 425 can regulate gas flow into and out of one side ofthe chamber 416. In one aspect, gas flow to and from the opposite sidesof the piston 417 in the potential energy storage mechanism 413 can becontrolled with the example valves illustrated in FIGS. 3A-3C to changethe properties of the potential energy storage mechanism 413 and/orreconfigure the potential energy storage mechanism 413 for other uses orfunctions.

Thus, in one aspect, a spring rate of the potential energy storagemechanism 413 can be dynamically variable by changing the gas pressurein the chamber by controlling the valves 424, 425. Once a desiredpressure or spring rate has been achieved, both the valves 424, 425 canbe closed to maintain the pressure for as long as desired, such as along period of time. In another aspect, a zero position of the potentialenergy storage mechanism 413 can be dynamically variable by controllingthe valves 424, 425 to move the piston to a desired location within thechamber. In yet another aspect, the potential energy storage mechanism413 can serve as a pneumatic damper by controlled release of gas fromthe chamber using the valves 424, 425. Additionally, the pneumaticspring can be configured to selectively function as a pneumatic actuatorby controlling the valves 424, 425 to move the piston within thechamber. When thus utilized, the pneumatic actuator can serve tosupplement the primary actuator 412. The pneumatic spring can also beconfigured to facilitate free movement of the piston, by control of thevalves, to selectively disengage the pneumatic spring/actuator/damper.Coordinated operation of the valves 424, 425 can therefore control thepneumatic spring to function in a variety of ways. The pneumatic springand valve configuration, along with the actuator, can perform functionssimilar to those described above with reference to FIGS. 2A and 2B. Forexample, the hydraulic actuator and the pneumatic spring can both bedisengaged to facilitate free movement of support members relative toone another, such as during a swing phase of a walking gait. The use offluids in a hydraulic actuator and a pneumatic spring can thereforefacilitate dynamic recruiting and tuning (e.g., energy inputcapability), to optimally provide potential energy storage/recovery andactuation consistent with any given application or demand scenario.

As with FIG. 2B, the configuration of FIG. 20 can be used to allowpotential energy to be stored and recovered during part of a gait cycle,and permit support members to follow a quasi-ballistic (passivedynamics) torque versus joint angle trajectory (e.g. during leg swing).In one aspect, spring characteristics, damping characteristics, and/orenergy input/extraction can be tunable to achieve a desired result in asingle gait cycle. Although this configuration can be utilized at anysuitable location, this configuration can be utilized effectively fordegrees of freedom corresponding to knee flexion/extension and/or hipflexion/extension due to the ease of dynamically tuning compliance withthis configuration. FIG. 20 also illustrates an additional oralternative potential energy storage mechanism 413′, which may be of anysuitable configuration described herein, arranged in series with theactuator 412. Thus, potential energy storage mechanisms can be arrangedin series and/or in parallel with an actuator at any given joint.

In one aspect, the actuator and potential energy storage mechanismdisclosed herein can provide the ability to adapt to any given situationor loading scenario by dynamically altering the characteristics of thecombination of damping, energy storage/recovery, and actuation to createan optimal load-carrying capability for the legged robotic device.Accordingly, control policies and software can be utilized that can takeadvantage of the energy recovery, and power reduction capabilities ofactuator and potential energy storage mechanisms of the legged roboticdevice.

FIGS. 3A-30 illustrate several examples of valve arrangements that canbe used to control hydraulic and/or pneumatic components of a leggedrobotic device as disclosed herein. Other valve configurations andarrangements are possible and it should be recognized that any suitablevalve configuration or arrangement may be utilized. FIG. 3A illustratesa configuration utilizing a pair of three-way valves 520, 521 to controlfluid flow between a pressure source and return and to opposite A and Bsides of a piston in a chamber. In this case, the three-way valves 520,521 can supply pressurized fluid as desired to the A and/or B sides of ahydraulic actuator or a pneumatic potential energy storage mechanism.The three-way valves 520, 521 can also control fluid flow from the A andB sides to provide damping, modify a zero position of the potentialenergy storage mechanism, facilitate disengagement of the actuator orpotential energy storage mechanism to facilitate free swinging ofsupport members, etc.

FIG. 3B illustrates a configuration utilizing a pair of three-way valves620, 621 and a two-way valve 622 to control fluid flow between apressure source and return and to opposite A and B sides of a piston ina chamber. This configuration is similar to the configurationillustrated in FIG. 3A, with the addition of the two-way valve 622.Thus, the three-way valves 620, 621 can supply pressurized fluid asdesired to the A and/or B sides of a hydraulic actuator or a pneumaticpotential energy storage mechanism. In this case, by closing thethree-way valves 620, 621, the two-way valve 622 can facilitate fluidmovement between the A and B sides to provide damping, modify a zeroposition of the potential energy storage mechanism, facilitatedisengagement of the actuator or potential energy storage mechanism tofacilitate free swinging of support members, etc.

FIG. 3C illustrates a configuration utilizing a four-way valve 723 and atwo-way valve 722 to control fluid flow between a pressure source andreturn and to opposite A and B sides of a piston in a chamber. In thiscase, the four-way valve 723 can supply pressurized fluid as desired tothe A and/or B sides of a hydraulic actuator or a pneumatic potentialenergy storage mechanism (e.g., a pneumatic actuator that can also actas a potential energy storage mechanism). In this case, by closing thefour-way valve 723, the two-way valve 722 can facilitate fluid movementbetween the A and B sides to provide damping, modify a zero position ofthe potential energy storage mechanism, facilitate disengagement of theactuator or potential energy storage mechanism to facilitate freeswinging of support members, etc.

Each of these valve configurations can allow fluid to be shunted in acontrolled way, such that support members are capable of swingingfreely. In addition, these valve configurations can facilitate lockingsupport members relative to one another, dissipating energy in acontrolled way (i.e., by acting as a damper), and/or storing energy in apotential energy storage mechanism, without drawing power from thepressurized fluid supply, which is unlike a traditional four-way valveused to modulate power/fluid flow in a hydraulically actuated jointwhere work is done by the pressurized fluid supply to accelerate ordecelerate support members about a joint. Thus, an advantage of thevalve configurations disclosed herein is that the natural dynamics ofthe robotic device can be utilized to reduce power usage. Anotheradvantage of the valve configurations disclosed herein is that anactuator can be recruited in real-time with the valves acting as adigital transmission, which can also contribute to improving powerefficiency.

FIG. 4 is a graph of a typical human walking gait cycle for the kneejoint, in particular, the relationship between knee torque and kneeangle (see, e.g., K. Shamaei, G. S. Sawichi, and P. M. Dollar, PLOS ONE,Vol. 8(3):e59993 (2013)). The start and end point at A corresponds tosuccessive heel strike of the same foot. During the stance phase, thejoint torque versus joint angle has a spring-like behavior with the kneeacting as a shock absorber, while during the swing phase the knee has aquasi-ballistic (passive dynamics) response with some damping during thefinal extension that take place before heel strike. During the stancephase (from heel strike at point A to toe-roll/terminal stance at pointD) the torque-joint profile has a quasi-elastic behavior. The dynamicstiffness changes with load and walking or running speed, but thespring-like behavior is qualitatively preserved. During the swing phaseof the walk cycle (from roll/terminal stance at point D to heel strikeat point A), the trajectory is quasi-ballistic and the knee primarilyacts as a controlled damper. The technology disclosed herein can beconfigured to exploit these features to minimize demands on the poweredactuators, and to reduce overall power usage. For example, an actuatorand/or can exploit the quasi-elastic response of the knee during thestance phase of walking, and other unique characteristics of hip andthigh joints to create an actuation system that is lightweight andefficient. A degree of freedom corresponding to knee flexion/extensioncan include a tunable potential energy storage mechanism that operatesin parallel with a primary (tunable) hydraulic actuator, such as isillustrated in FIGS. 2B and 2C discussed above, and can operate in amanner similar to the walking gait cycle illustrated in FIG. 4. Forexample, the potential energy storage mechanism and hydraulic actuatorcan be dynamically tuned or adjusted to provide the spring-like behaviorcharacteristics of the stance phase, as well as the free-swinging anddamping characteristics of the swing phase.

FIGS. 5A and 5B illustrate a legged robotic device 800 in accordancewith another example of the present disclosure. The legged roboticdevice 800 can include a support member 810 a coupled to a supportmember 810 b for relative movement defining a degree of freedomcorresponding to a degree of freedom of a hip of a human leg. Forexample, the support members 810 a, 810 b can be rotatably coupledtogether defining a rotational degree of freedom about axis 811 a, whichcan correspond to a hip flexion/extension degree of freedom. The leggedrobotic device 800 can also include an actuator 812 a to apply a torqueto the support members 810 a, 810 b in the degree of freedom about theaxis 811 a. In addition, a potential energy storage mechanism 813 a canbe associated with the degree of freedom about the axis 811 a andoperable to store potential energy as a result of relative movement ofthe support members 810 a, 810 b in the degree of freedom and to provideat least a portion of the stored potential energy to the support members810 a, 810 b as a compensating torque to assist the actuator 812 a. Aspring rate and/or a zero position of the potential energy storagemechanism 813 a can be dynamically variable. In one aspect, the supportmember 810 b can be resiliently flexible sufficient to form a degree offreedom corresponding to a degree of freedom of a knee of a human leg,such as knee flexion/extension. The resiliently flexible support member810 b can be operable to store potential energy as a result of bendingthe support member 810 b and to provide at least a portion of the storedpotential energy to straighten the support member 810 b.

In one aspect, the resiliently flexible support member 810 b can serveas a potential energy storage mechanism in the form of a bendable spring(bow spring), which can extend from the hip joint (where it is coupledthereto) down to underneath the foot capable of supporting a verticalload and transferring the vertical load through the bottom underneaththe foot. In one aspect, the resiliently flexible support member 810 bcan have a forward pre-bend to facilitate bending in a desired directionand at a desired location, such as proximate the user's knee. In anupright position or non-energized state, the user or wearer would notfeel the load as the load is transferred through the support member 810b or potential energy storage mechanism to the ground. As the supportmember 810 b or potential energy storage mechanism is energized (e.g.,when the wearer bends down), energy is put into the potential energystorage mechanism. Upon release, or upon the user standing upright, theenergy is recovered, and put back into the load. This is one example ofa situation where a potential energy storage mechanism can be used toreduce the amount of work done by the robotic device. In other words,the user is using his gravity induced weight to put energy into thepotential energy storage mechanism. When it is desired to get the energyback, the user stands or otherwise moves to de-energize the potentialenergy storage mechanism so now the amount of work the user needs to dois reduced by the amount of energy put into the potential energy storagemechanism.

In one aspect, the legged robotic device 800 can include a tendon 830,such as a cable, coupled to the resiliently flexible support member 810b via a series of eyelets 831 a-c and terminating at a leverage arm 832extending from the resiliently flexible support member 810 b. The tendon830 can be coupled to an actuator 812 b located proximate the hip of theuser and/or the actuator 812 a. The actuator 812 b can be any suitabletype of actuator as described herein. The actuator 812 b can pull on thetendon 830, which can in turn pull on the leverage arm 832 to produce atorque that can bend the resiliently flexible support member 810 b in adegree of freedom corresponding to knee flexion/extension. Thus, thenumber and location of the eyelets 831 a-c, and the length and locationof the leverage arm 832 can be selected to produce a desired amount ofbending of the resiliently flexible support member 810 b for a givenamount of tension in the tendon 830 and to cause bending of theresiliently flexible support member 810 b at a desired location.

In accordance with one embodiment of the present invention, a method forproviding a compensating torque to assist an actuator of a leggedrobotic device is disclosed. The method can comprise providing aplurality of support members coupled together for relative movementdefining a plurality of degrees of freedom, at least one of theplurality of degrees of freedom corresponding to at least one degree offreedom of a human leg. The method can also comprise providing anactuator to apply a force or a torque to the support members in the atleast one of the plurality of degrees of freedom. Additionally, themethod can comprise providing a potential energy storage mechanismassociated with the at least one of the plurality of degrees of freedomoperable to store potential energy as a result of relative movement ofthe support members in the at least one of the plurality of degrees offreedom and to provide at least a portion of the stored potential energyto the support members as a compensating force or torque to assist theactuator, wherein at least one of a spring rate and a zero position ofthe potential energy storage mechanism is dynamically variable. It isnoted that no specific order is required in this method, thoughgenerally in one embodiment, these method steps can be carried outsequentially.

In one aspect of the method, the actuator can be undersized for amaximum load requirement without the existence of the potential energystorage mechanism. In another aspect of the method, the at least onedegree of freedom of the human leg can comprise at least one of hipflexion/extension, hip abduction/adduction, hip medial/lateral rotation,knee flexion/extension, ankle flexion/extension, ankleinversion/eversion, and ankle medial/lateral rotation. In yet anotheraspect of the method, the potential energy storage mechanism cancomprise a tension spring, a compression spring, a torsion spring, aspiral torsion spring, a pneumatic spring, a cantilever spring, aconstant force spring, a negator spring, an elastomeric material, avolute spring, a coil spring, a flat spring, a bow spring, or acombination thereof.

It is to be understood that the embodiments of the invention disclosedare not limited to the particular structures, process steps, ormaterials disclosed herein, but are extended to equivalents thereof aswould be recognized by those ordinarily skilled in the relevant arts. Itshould also be understood that terminology employed herein is used forthe purpose of describing particular embodiments only and is notintended to be limiting.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as de factoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thedescription, numerous specific details are provided, such as examples oflengths, widths, shapes, etc., to provide a thorough understanding ofembodiments of the invention. One skilled in the relevant art willrecognize, however, that the invention can be practiced without one ormore of the specific details, or with other methods, components,materials, etc. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringaspects of the invention.

While the foregoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

What is claimed is:
 1. A legged robotic device, comprising: a pluralityof support members coupled together for relative movement about arespective plurality of joints defining a plurality of degrees offreedom, at least one of the plurality of degrees of freedomcorresponding to at least one degree of freedom of a human leg; aprimary actuator to apply a force or a torque to the support members inthe at least one of the plurality of degrees of freedom; a potentialenergy storage mechanism in the form of a fluid spring having a chamberand a piston moveable within the chamber, the fluid spring beingassociated with the at least one of the plurality of degrees of freedomoperable to store potential energy as a result of relative movement ofthe support members in the at least one of the plurality of degrees offreedom and to provide at least a portion of the stored potential energyto the support members as a compensating force or torque to assist theprimary actuator, wherein at least one of a zero position or a preloadof the potential energy storage mechanism is dynamically variable; andat least one valve in fluid communication with the fluid spring, andoperable to control movement of the piston of the fluid spring byregulating fluid flow into and out of the chamber on opposing sides ofthe piston, wherein the fluid spring and the at least one valve areoperable to dynamically vary the at least one of the zero position orthe preload of the potential energy storage mechanism during operation.2. The legged robotic device of claim 1, wherein the primary actuator isundersized for a maximum load requirement without the existence of thepotential energy storage mechanism.
 3. The legged robotic device ofclaim 1, wherein the at least one degree of freedom of the human legcomprises at least one of hip flexion/extension, hipabduction/adduction, hip medial/lateral rotation, kneeflexion/extension, ankle flexion/extension, ankle inversion/eversion, orankle medial/lateral rotation.
 4. The legged robotic device of claim 1,wherein the primary actuator comprises at least one of a hydraulicactuator, a pneumatic actuator, or an electric actuator.
 5. The leggedrobotic device of claim 1, wherein the primary actuator and thepotential energy storage mechanism are arranged in parallel.
 6. Thelegged robotic device of claim 1, wherein the primary actuator comprisesa hydraulic actuator.
 7. The legged robotic device of claim 6, whereinthe hydraulic actuator is configured to selectively function as ahydraulic damper.
 8. The legged robotic device of claim 6, wherein thehydraulic actuator is configured to facilitate free movement of a pistonof the hydraulic actuator to selectively disengage the hydraulicactuator, and wherein selective disengagement of the fluid spring andthe hydraulic actuator facilitate free relative movement of the supportmembers in the at least one of the plurality of degrees of freedom. 9.The legged robotic device of claim 6, wherein the fluid spring comprisesa pneumatic spring configured to facilitate free movement of a piston ofthe pneumatic spring to selectively disengage the pneumatic spring,wherein the hydraulic actuator is configured to facilitate free movementof a piston of the hydraulic actuator to selectively disengage thehydraulic actuator, and wherein selective disengagement of the pneumaticspring and the hydraulic actuator facilitate free relative movement ofthe support members in the at least one of the plurality of degrees offreedom.
 10. The legged robotic device of claim 9, wherein free movementof the piston of the hydraulic actuator is controlled by at least onevalve.
 11. The legged robotic device of claim 1, wherein at least one ofa zero position or a spring rate of the fluid spring is dynamicallyvariable.
 12. The legged robotic device of claim 1, wherein the fluidspring comprises a hydraulic spring.
 13. The legged robotic device ofclaim 1, wherein the fluid spring comprises a pneumatic springconfigured to selectively function as at least one of a pneumaticactuator or a pneumatic damper.
 14. The legged robotic device of claim13, wherein the pneumatic spring is configured to facilitate varying atleast one of a spring rate, a zero position, or a preload of thepneumatic spring.
 15. The legged robotic device of claim 1, furthercomprising a damper to resist movement of the support members in the oneor more degrees of freedom.
 16. The legged robotic device of claim 15,wherein the damper comprises at least one of a hydraulic damper, apneumatic damper, a mechanical damper, or an electrical damper.
 17. Thelegged robotic device of claim 15, wherein a damping coefficient of thedamper is dynamically variable.
 18. The legged robotic device of claim1, further comprising a power source supported about the robotic deviceto power the actuator.
 19. The legged robotic device of claim 1, whereinthe legged robotic device is configured as an exoskeleton structure forattachment to a human body.
 20. The legged robotic device of claim 1,wherein the legged robotic device is configured as a humanoid robot. 21.The legged robotic device of claim 1, wherein the at least one valvecomprises a first valve in fluid communication with the fluid spring,and operable to control movement of the piston of the fluid spring byregulating fluid flow into and out of the chamber on opposing sides ofthe piston, and a second valve in fluid communication with the fluidspring, a pressure source and a return, wherein operation of the firstand second valves can be coordinated to dynamically vary the operationand function of the fluid spring.
 22. The legged robotic device of claim1, wherein the fluid spring and the at least one valve are configurableto cause the fluid spring to function as an actuator.
 23. The leggedrobotic device of claim 1, wherein the fluid spring and the at least onevalve are configurable to cause the fluid spring to function as adampener.
 24. The legged robotic device of claim 1, wherein the fluidspring and the at least one valve are configurable to facilitate freemovement of the piston to selectively disengage the fluid spring. 25.The legged robotic device of claim 1, further comprising a secondpotential energy storage mechanism arranged in at least one of parallelor series with the primary actuator.
 26. A legged robotic device,comprising: a first support member coupled to a second support memberfor relative movement defining a first degree of freedom correspondingto a degree of freedom of a knee of a human leg; a first primaryactuator to apply a force or a torque to the first and second supportmembers in the first degree of freedom; and a first potential energystorage mechanism in the form of a fluid spring having a chamber and apiston moveable within the chamber, the fluid spring being associatedwith the first degree of freedom operable to store potential energy as aresult of relative movement of the first and second support members inthe first degree of freedom and to provide at least a portion of thestored potential energy to the first and second support members as acompensating force or torque to assist the first primary actuator,wherein at least one of a zero position or a preload of the firstpotential energy storage mechanism is dynamically variable; and at leastone valve in fluid communication with the fluid spring, and operable tocontrol movement of the piston of the fluid spring by regulating fluidflow into and out of the chamber on opposing sides of the piston,wherein the fluid spring and the at least one valve facilitatedynamically varying the at least one of the zero position or the preloadof the potential energy storage mechanism during operation.
 27. Thelegged robotic device of claim 26, further comprising: a third supportmember coupled to the second support member for relative movementdefining a second degree of freedom corresponding to a degree of freedomof a hip of a human leg; a second primary actuator to apply a force or atorque to the second and third support members in the second degree offreedom; and a second potential energy storage mechanism in the form ofa spring associated with the second degree of freedom operable to storepotential energy as a result of relative movement of the second andthird support members in the second degree of freedom and to provide atleast a portion of the stored potential energy to the second and thirdsupport members as a compensating force or torque to assist the secondprimary actuator.
 28. The legged robotic device of claim 27, wherein thedegree of freedom of the hip comprises at least one of hipflexion/extension, hip abduction/adduction, or hip medial/lateralrotation.
 29. The legged robotic device of claim 27, further comprising:a fourth support member coupled to the third support member for relativemovement defining a third degree of freedom corresponding to a seconddegree of freedom of the hip; a third primary actuator to apply a forceor a torque to the third and fourth support members in the third degreeof freedom; and a third potential energy storage mechanism in the formof a spring associated with the third degree of freedom operable tostore potential energy as a result of relative movement of the third andfourth support members in the third degree of freedom and to provide atleast a portion of the stored potential energy to the third and fourthsupport members as a compensating force or torque to assist the thirdprimary actuator.
 30. The legged robotic device of claim 29, furthercomprising: a fifth support member coupled to the fourth support memberfor relative movement defining a fourth degree of freedom correspondingto a third degree of freedom of the hip; a fourth primary actuator toapply a force or a torque to the fourth and fifth support members in thefourth degree of freedom; and a fourth potential energy storagemechanism in the form of a spring associated with the fourth degree offreedom operable to store potential energy as a result of relativemovement of the fourth and fifth support members in the fourth degree offreedom and to provide at least a portion of the stored potential energyto the fourth and fifth support members as a compensating torque toassist the fourth primary actuator.
 31. A legged robotic device,comprising: a first support member coupled to a second support memberfor relative movement defining a first degree of freedom correspondingto a degree of freedom of a hip of a human leg, the second supportmember being resiliently flexible sufficient to form a second degree offreedom corresponding to a degree of freedom of a knee of the human leg;an actuator to apply a torque to the first and second support members inthe first degree of freedom; and a potential energy storage mechanismassociated with the first degree of freedom operable to store potentialenergy as a result of relative movement of the first and second supportmembers in the first degree of freedom and to provide at least a portionof the stored potential energy to the first and second support membersas a compensating torque to assist the actuator, wherein the resilientlyflexible second support member is operable to store potential energy asa result of bending the second support member and to provide at least aportion of the stored potential energy to straighten the second supportmember.
 32. The legged robotic device of claim 31, wherein theresiliently flexible second support member is configured as a bowspring.
 33. The legged robotic device of claim 31, wherein theresiliently flexible second support member is operable to facilitatesupporting a vertical load and transferring the vertical load underneatha foot of a user.
 34. The legged robotic device of claim 31, wherein theresiliently flexible second support member comprises a forward pre-bendto facilitate bending in a predetermined direction at a locationproximate a user's knee.
 35. The legged robotic device of claim 31,further comprising a tendon coupled to the actuator and the resilientlyflexible second support member, wherein the actuator is operable to pullon the tendon, which pulls on the resiliently flexible second supportmember to facilitate bending of the resiliently flexible second supportmember.
 36. The legged robotic device of claim 35, wherein the tendoncomprises a cable.
 37. The legged robotic device of claim 35, whereinthe tendon is coupled to the resiliently flexible second support membervia a series of eyelets and terminates at a leverage arm extending fromthe resiliently flexible second support member.
 38. A method forproviding a compensating torque to assist an actuator of a leggedrobotic device, comprising: providing a plurality of support memberscoupled together for relative movement defining a plurality of degreesof freedom, at least one of the plurality of degrees of freedomcorresponding to at least one degree of freedom of a human leg;providing a primary actuator to apply a force or a torque to the supportmembers in the at least one of the plurality of degrees of freedom;providing a potential energy storage mechanism in the form of a fluidspring having a chamber and a piston moveable within the chamber, thefluid spring being associated with the at least one of the plurality ofdegrees of freedom operable to store potential energy as a result ofrelative movement of the support members in the at least one of theplurality of degrees of freedom and to provide at least a portion of thestored potential energy to the support members as a compensating forceor torque to assist the primary actuator, wherein at least one of a zeroposition or a preload of the potential energy storage mechanism isdynamically variable; and providing at least one valve in fluidcommunication with the fluid spring for controlling movement of thepiston of the fluid spring by regulating fluid flow into and out of thechamber on opposing sides of the piston, and for facilitatingdynamically varying the at least one of the zero position or the preloadof the potential energy storage mechanism during operation.
 39. Themethod of claim 38, wherein the primary actuator is undersized for amaximum load requirement without the existence of the potential energystorage mechanism.
 40. The method of claim 38, wherein the at least onedegree of freedom of the human leg comprises at least one of hipflexion/extension, hip abduction/adduction, hip medial/lateral rotation,knee flexion/extension, ankle flexion/extension, ankleinversion/eversion, or ankle medial/lateral rotation.
 41. The method ofclaim 38, wherein the fluid spring comprises at least one of a pneumaticspring or a hydraulic spring.